The aim of the Collaborative Study of the Genetics of Asthma is to identify asthma susceptibility loci. At each center families were ascertained through 2 siblings with asthma. Using that genetic data and with recruitment of additional asthmatics and their parents, we will be able to identify asthma susceptibility genes and their variants, interactions with other genes and environmental risk factors, as well as provide insight for the development of improved treatment and ultimate prevention of asthma.